The present invention relates to a refrigerated container apparatus having a refrigeration unit which permits inflow of air for cooling from multiple directions to diffuse frost buildup. The invention relates particularly to refrigerated display cabinets which have access openings therein and thus are particularly susceptible to frost buildup. The improved evaporator unit comprises a cooling tube core and associated housing panels for positioning within the refrigerated apparatus.
Commercial refrigerated apparatus have heat extracted by evaporator units. These units are connected as part of a refrigeration circuit comprised of one or more compressors, a condenser system, a receiver, an expansion valve, and one or more evaporators. The refrigerated is compressed by the compressors and pumped through the circuit in the above order as a high pressure gas from the compressor to the condenser system and thereafter is handled as a high pressure liquid until it is expanded to a lower pressure through the expansion valve. The low pressure side extends from the expansion valve through the evaporators to the suction intake of the compressor.
In refrigerated display units air is utilized as a medium of heat exchange between the evaporator unit and the products to be maintained at a low temperature. In refrigerated apparatus where barrier doors are utilized to separate the cooled air within the apparatus from the moist ambient air, refrigeration cycles can extend for long periods with only occasional defrosting cycles in order to clear the evaporator coils from the frost and ice buildup.
In refrigerated apparatus where frequent entry is made into the apparatus for the placement of products to be cooled and for extraction of products as in retail food stores frost and ice buildup in the evaporator units can be quite rapid. Typically two defrost cycles are required per day for removing the frost and ice from the evaporator units in such apparatus. The problem of ice and frost formation is particularly acute in those refrigerated apparatus having access openings through which store personnel stock products into the apparatus and through which customers remove product. In these apparatus a refrigerated air band is circulated from an air outlet across the access opening to an air inlet and thereafter is propelled through an internal air conduit and into contact with the evaporator unit in order to cool the same. Variations of such apparatus permit one or more secondary and guard air bands to be used to further protect the refrigerated air band against contact with the ambient moist air. These additional air bands while helpful, still do not sufficiently protect the refrigerated air band to sufficiently reduce the frequency of defrost cycles to an optimum low level.
In the operation of all types of refrigerated display cabinets, it is desirable to include a system for automatically defrosting the evaporator unit. The defrost cycle can be actuated either at set periodic time intervals. Or when the frost buildup within the system has reached a certain predetermined level. Such latter type of systems are typically thermostatically controlled so as to switch from a refrigerated cycle to a defrost cycle of operation.
There have been three different approaches for defrosting refrigerated apparatus in this art. These are utilizing electric resistance heaters; passing a compressed refrigerant gas having a high specific heat content through the refrigeration coils; and, circulating ambient air through an air conduit in which the refrigeration coils are positioned. Due to the increased cost of energy, wide spread efforts have been made to place more emphasis on the utilization of ambient air defrost systems as an alternative to the electrical resistance heaters or compressed refrigerant gas defrost systems.
Barrier doors have been used in refrigerated apparatus in order to reduce the contact between the ambient air and the internally circulated refrigerated air band. Representative U.S. Patents are U.S. Pat. Nos. 4,265,090 to Ibrahim and 4,312,190 to Ibrahim and Perez. In some refrigerated display cases having barrier doors multiple air bands are employed for additional protection for the refrigerated air band as exemplified by U.S. Pat. Nos. 4,299,092, 4,369,631 and 4,369,632 all, to Ibrahim.
As shown by FIG. 2 of U.S. Pat. No. 4,312,190, the flow of refrigerated air through the evaporator coils in these units is in a single direction from the front end to the back end in the direction of the refrigerated air band flow. This flow pattern for the refrigerated air band results in the front end of the evaporator coils becoming heavily coated with frost and ice whereby the air flow is reduced. Upon the accumulation of sufficient frost and ice the air flow through the evaporator coils is greatly reduced at which time the cooling capacity of the refrigerated apparatus is seriously decreased. A defrost cycle must then be initiated in order to clear the evaporator coils of the accumulated ice and frost.
The evaporator coil units used for cooling the air bands in the above refrigeration apparatus are constructed by placing a cooling tube core which consists of one or more serpentine arranged refrigerant tubes within a series of parallel arranged cooling fins. This core unit is then surrounded by housing panels which provide for air flow therethrough in planes parallel to the planes established by the cooling fins. This type of arrangement is shown in U.S. Pat. No. 4,361,012, FIGS. 4 and 5, to Ibrahim. In these units the housing panels wall off any inflow of the air band from portions of the cooling tube core other than the front and top sides which are perforated. The use of perforated housing panels for the cooling tube core permits a wider distribution of the air contact with the cooling tube core elements but results in air blockage at the perforation openings due to buildup of ice and frost on the fins immediately under the perforations. This type of cooling tube core arrangement is also illustrated in FIGS. 18 and 19 of U.S. Pat. No. 4,369,632, mentioned above.
In one employment the housing panels have been removed from portions of the cooling tube core in order to permit cross flow of air bands into contact with a portion of the evaporator coils in order to create a cooled secondary air band as shown in U.S. Pat. No. 4,389,852 to Ibrahim. As shown in this patent the lower portion 36 of the evaporator coils is exposed to cross flow by a secondary band. In this arrangement the entire air band does not exit through the opposite end of the cooling tube core and there are no guide panels associated with the core which distribute the incoming air band to be cooled over a substantial length of the cooling tube core in the direction of air band movement. The main ice and frost accumulation in this type of unit is in the lower portion 36 of the cooling coils rather than distributed through the cooling coils and fins in the evaporator unit 24.
Japanese Published Patent Application No. 52 32154 shows a cooling tube core arrangement in which the air band is diffused for better heat exchange contact with the cooling tubes and fins. The primary ice and frost accumulation in this unit will be at the lower end of the tube core and will not be distributed along the longitudinal length of the tube core in the direction of air band flow due to the suspension brackets which limit flow along the sides of the cooling tube core.
U.S. Pat. No. 3,898,864 shows a plenum chamber which functions to permit continued air flow when the primary coil inlet becomes frosted closed. A host collection cavity is provided which would result in incomplete defrosting if reverse defrost air flow were to be used.
Other patents which show refrigerator coils not designed for reverse defrost flow are U.S. Pat. Nos. 2,152,291 and 3,364,696. U.S. Pat. No. 3,147,602 which discloses an evaporator designed for frost distribution does not show air defrost or reverse defrost air flow means.
In refrigerated apparatus which have conventional multiple separated cooling tube cores it is the cooling core which is first contacted by the refrigerated air which develops the ice and frost which then eventually constricts the air passages and requires the initiation of a defrost cycle. U.S. Pat. No. 4,369,631 shows a number of case constructions with multiple cooling tube elements. In FIGS. 10-13 it is evaporator 424 which will encounter the greatest problem with respect to the need for defrost.
The improved evaporator unit of the present invention is designed to function as the initial contact unit for a circulated air band. This improved unit diffuses the frost and ice buildup over a large area within the cooling tubes and fins since the air band inward flow is from at least two and, preferably, a plurality of directions along a substantial length of the cooling tube core in the direction of air band flow.
Another feature of the present invention is the utilization of a staggered cooling fin arrangement which then places the ice and frost accumulation on the leading edge of adjacent fins at different longitudinal positions. A preferred feature is to employ a heating source which can direct heat radiant energy into the cooling core tubes and fins during a defrost cycle.